Problem understanding how to UV unwrap for bump and color material
You can add up to 8 UVMaps in the Object Data Properties panel and use them independently in the Shader Editor. As you can read in the manual, each UVMap contains every face of the model, so if you wont unwrap any of them they will be at the bottom left corner in the UV Editor, so those whole faces will get the value of the bottom left pixel of the texture image. So I don't think this would be the optimal way for you. May be it would be better if you create a mask for the bump map.